Hi

You can't use a cells address as name for functions, you intend to use in the worksheet itself. Though it works in your Sub Test(), you should generally avoid using names already excel has in use. This may cause problems, or as you see in your case errors.

In Versions 2007 and above ODE45 refers to the cell of column 10249, row 45 and is therefore in use of Excel itself.
Your function as it is will work perfectly in Versions up to 2003.